1. Field of the Invention
The present invention relates generally to wireless charging, and more particularly, to a method for preventing an abnormality during wireless charging.
2. Description of the Related Art
In view of their nature, mobile terminals such as portable phones and Personal Digital Assistants (PDAs) are powered by rechargeable batteries. To charge the batteries, the mobile terminals apply electrical energy to the batteries via chargers. Typically, the charger and the battery each have an exterior contact terminal and thus are electrically connected to each other by contacting their contact terminals.
This contact-based charging scheme faces the problem of vulnerability of contact terminals to contamination by foreign materials and the resulting unreliable battery charging because the contact terminals protrude outward. Moreover, if the contact terminals are exposed to moisture, the batteries may not be charged properly.
To address the above problem, wireless charging or contactless charging has recently been developed and applied to many electronic devices.
Such wireless charging is based on wireless power transmission and reception. For example, once a portable phone is placed on a charging pad without being connected to an additional charging connector, its battery is automatically charged. Among wirelessly charged products, wireless electric toothbrushes or wireless electric shavers are well known. Wireless charging offers the benefits of increased waterproofness due to wireless charging of electronic products and enhanced portability due to no need for a wired charger for electronic devices. Further, it is expected that wireless charging will be more developed for electric vehicles.
There are three wireless charging schemes: electromagnetic induction using coils, resonance-based wireless charging, and Radio Frequency (RF)/microwave radiation based on the conversion of electrical energy to microwaves.
To date, the electromagnetic induction-based wireless charging scheme has been most popular. However, considering recent successful experiments in wireless power transmission over microwaves at a distance of tens of meters in Korea and other overseas countries, it is foreseeable that every electronic product will be charged wirelessly at any time in any place in the near future.
Electromagnetic induction-based power transmission refers to power transfer between primary and secondary coils. When a magnet moves through a coil, current is induced. Based on this principle, a transmitter creates a magnetic field and a receiver produces energy by current induced by a change in the magnetic field. This phenomenon is called magnetic induction and power transmission based on magnetic induction is highly efficient in energy transfer.
A resonance-based wireless charging system has achieved wireless energy transfer from a charger at a distance of a few meters based on the resonance-based power transmission principle by the Coupled Mode Theory. The resonated electromagnetic waves carried electric energy instead of sound. The resonant electrical energy is directly transferred only in the presence of a device having the same resonant frequency, while the unused electrical energy is reabsorbed into the electromagnetic field rather than being dispersed into the air. Thus, the resonant electrical energy does not affect machines or human beings, as compared to other electronic waves.
Wireless charging is an active research area. Thus, there is a need for developing a standard regarding wireless charging priority, detection of a wireless power transmitter/receiver; communication frequency selection between a wireless power transmitter and a wireless power receiver, wireless power control, selection of a matching circuit, and allocation of a communication time to each wireless power receiver in a single charging cycle. Particularly, there exists a need for developing standards for a configuration and procedure that allow a wireless power receiver to select a wireless power transmitter from which to receive wireless power.
A single wireless power transmitter can supply charging power to a plurality of wireless power receivers. Because the plurality of wireless power receivers are different in terms of characteristics, states, and types, various algorithms may be performed to determine transmission power of the wireless power transmitter.
If an abnormality occurs in at least one wireless power receiver during wireless charging with transmission power determined according to a specific algorithm in the wireless power transmitter, the wireless charging may fail.
For example, a wireless power transmitter or a wireless power receiver may be placed in an error situation such as overvoltage, overcurrent, or overtemperature due to a specific algorithm or some defect in the wireless power receiver.
If the error situation is not self-corrected, the wireless power transmitter may enter a latch fault mode in which it is powered off and prompts a user to reset it, in order to protect the wireless power transmitter or each wireless power receiver which is being charged.
However, if the wireless power transmitter enters the latch fault mode, the user is required to solve the problem, which is not favorable in terms of User eXperience (UX).
Accordingly, there is a need for a self-correcting method for preventing an abnormal situation from developing to an extreme in a system.